Prevalence and implications of sex reversal in free-living birds

The ability to unequivocally identify the sex and reproductive status of individuals is crucial across many fields of study. Recent evidence indicates that avian sex determination is more flexible than once believed, with sex-reversed individuals identified in domestic bird populations—that is, individuals exhibiting gonadal and morphological traits of one sex while possessing the chromosomal makeup of the opposite sex. The presence of these individuals can challenge the reliability of traditional sexing methods that rely solely on external morphology, internal anatomy, or genetic markers. These methods, when used in isolation, fail to identify sex-reversed or intersex individuals, potentially overlooking their impact on population dynamics. In this pioneering study, we investigated the prevalence of sex-reversed individuals in five common free-living avian species in Queensland, Australia. By comparing internal and external morphological characteristics with PCR results from sex-linked molecular markers, we identified sex-reversed individuals in all five species, with rates ranging from 3% to 6%. Our findings suggest that sex reversal is a common and potentially widespread phenomenon in avian species.

精准明确地鉴定个体的性别与生殖状态，这一能力在诸多研究领域中均具有关键意义。近期研究证据表明，鸟类的性别决定机制比此前认知更为灵活，在家禽种群中已发现性反转个体——即呈现出某一性别的性腺与形态学特征，但却携带另一性别的染色体组型的个体。这类个体的存在，会对仅依赖外部形态、内部解剖结构或遗传标记的传统性别鉴定方法的可靠性构成挑战。此类方法若单独使用，将无法识别性反转或间性个体，进而可能忽视其对种群动态的影响。在本项开创性研究中，我们针对澳大利亚昆士兰州的5种常见野生鸟类展开调查，统计了其中性反转个体的检出率。通过比对个体的内外形态学特征与基于性别连锁分子标记的聚合酶链式反应（Polymerase Chain Reaction, PCR）检测结果，我们在全部5个物种中均发现了性反转个体，其检出率介于3%至6%之间。本研究结果表明，性反转现象在鸟类中普遍存在，且可能是一项广泛分布的生物学现象。